The present invention relates to a system for recording signals on a disc-type rotary recording medium (hereinafter simply referred to as a disc) such as a magnetic disc, optical disc or photoelectromagnetic disc.
With known systems of the type which records signals on a recording medium such as a magnetic disc while rotating the disc by a motor, a method of controlling the rotational phase of the motor in accordance with the phase of a reference clock signal has been used (the method is hereinafter referred to as a phase control). While this phase control is capable of controlling the rotation velocity of the motor with a high degree of accuracy as compared with a method of detecting the rotation velocity of the motor to effect the rotation control (this method is hereinafter referred to as a velocity control), it has the disadvantage of requiring a longer time from the start of the motor until the rotation velocity is stabilized (this is hereinafter referred to as a lock-in condition) than in the case of the velocity control.
Then, in the case of a disc rotation control device which can be used with a small electronic still picture camera incorporating a recording system using, for example, a magnetic disc, a method is conceivable in which the phase of an output from a rotational phase signal generator (hereinafter referred to as a PG) which generates one or a plurality of pulses for every rotation of the magnetic disc is compared with the phase of a vertical synchronizing signal of a video signal to be recorded on the magnetic disc and the rotation control or the phase control of the magnetic disc driving motor is effected so as to maintain the phase difference between the two signals at a predetermined value. Taking for example the case of a portable appliance such as an electronic still picture camera, a battery is incorporated as a portable power supply and the capacity of the battery is limited. Therefore, a consideration should preferably be given so that the rotation of the disc is started just before the recording of a signal and the rotation is stopped upon the completion of the recording, thereby reducing the power consumption due to the rotation of the disc as far as possible. The measures heretofore taken for th:s purpose include, for example, the method of starting the rotation of the disc through the half-depression of the shutter button or the like in response to the action for photo taking purposes. In the case of this type of electronic still picture camera, no video is recorded during the time interval from the start of the rotation of the disc until the lock-in condition is attained and therefore the time interval between the start and the lock-in condition must be decreased as far as possible.
Also, in the case of portable type disc signal recording apparatus represented by a small electronic still picture camera incorporating, for example, the above-mentioned magnetic disc recording system, differing from stationary apparatus such as floppy disc drive apparatus or video disc apparatus, an object to be shot is followed with the disc drive unit itself being held with the hand and therefore the disturbance torque applied to the motor varies considerably thus giving rise to the danger that the rotation of the disc will deviate from the lock-in condition. In this case, also, no video is recorded, as during starting and therefore it is necessary to reduce as far as possible the time required for effecting the locking-in again after the locking-out or deviation.
Also, if, in the case of the phase control of the motor, the velocity control is effected as an auxiliary loop, some temperature drift of the velocity control circuit is compensated for by the phase control and thus the controlled velocity is not affected by the temperature. However, in order to control the rotation velocity of the motor so that it is substantially equal to the post lock-in velocity without effecting the phase control, it is necessary to construct a velocity control system of such high accuracy that the system is not affected by the temperature, etc.